The notion of landing astronauts on Mars has long been more fantasy than reality: The planet is, on average, 140 million miles from Earth, and its atmosphere isn’t hospitable to human life.

But a human voyage to the planet is now, for the first time, within the realm of possibility, according to space advocates inside and outside government. As a result, plans for a mission around the planet, and ultimately for lengthier stays, have been sprouting like springtime flowers.

The new momentum, some space experts say, comes from the successful landing of the large rover Curiosity in a Martian crater last year, the growing eagerness of space entrepreneurs to mount and fund missions to Mars and encouraging new data about the radiation risks of such an expedition.

NASA says it hopes to land astronauts on the planet within the next two decades, and the agency is developing a heavy-lift rocket and a new space capsule to achieve this goal. It has even established an optimal time frame for this event — in the early 2030s, when the very different orbits of the two planets brings them closest to each other.

[2] The Hundred Year Starship: The Nasa mission that will take astronauts to Mars and leave them there forever: http://www.prisonplanet.com/the-hundred-year-starship-the-nasa-mission-that-will-take-astronauts-to-mars-and-leave-them-there-forever.html

[3] The millionaire Dennis Tito and his mission to Mars: http://www.prisonplanet.com/the-millionaire-dennis-tito-and-his-mission-to-mars.html